Where is the lightest charmed scalar meson?

TL;DR

This paper challenges the traditional understanding of the lightest charmed scalar meson, proposing a lighter state at 2100 MeV instead of the commonly accepted 2300 MeV, based on analysis of LHCb data and chiral symmetry considerations.

Contribution

It introduces a unitarized chiral amplitude model that better fits experimental data, suggesting a lighter charmed scalar meson and emphasizing the importance of symmetry-consistent analysis.

Findings

The $D_0^*(2100)$ fits LHCb decay data better than the $D_0^*(2300)$.

The $D o D ext{pi}$ phase difference relates to intermediate $ ho^-$ exchange.

Chiral symmetry, unitarity, and analyticity are crucial for scalar meson analysis.

Abstract

The lightest charmed scalar meson is known as the $D_0^*(2300)$, which is one of the earliest new hadron resonances observed at modern $B$ factories. We show here that the parameters assigned to the lightest scalar $D$-meson are in conflict with the precise LHCb data of the decay $B^-\to D^+ \pi^- \pi^-$. On the contrary, these data can be well described by an unitarized chiral amplitude containing a much lighter charmed scalar meson, the $D_0^*(2100)$. We also extract the low-energy $S$-wave $D\pi$ phase of the decay $B^-\to D^+ \pi^- \pi^-$ from the data in a model-independent way, and show that its difference from the $D\pi$ scattering phase shift can be traced back to an intermediate $\rho^-$ exchange. Our work highlights that an analysis of data consistent with chiral symmetry, unitarity, and analyticity is mandatory in order to extract the properties of the ground-state scalar mesons in the singly heavy sector correctly, in analogy to the light scalar mesons $f_0(500)$ and $K_0^*(700)$.